Incandescent electric lamp



W. DUNKEL May 25, 1937.

INCANDESCENT ELECTRIC LAMP Filed Feb; 20, 1936 Inventor" Wilhelm Du kel, by Z1 6 A His Attorneg I Patented May 25, 1937 PATENT OFFICE lNCANDESCENT ELECTRIC LAMP Wilhelm Dunkel, Berlin-Tempelhoi, Germany,

assignor to General Electric Company, a corporation of New York Application;n February 20, 1936, Serial No. 64,967

Germany March 13, 1935 2 Claims.

My invention relates to incandescent electric lamps, and more particularly to incandescent lamps having a resistance in series with the filamen It has heretofore been proposed to connect a resistance in series with the filament of an incandescent lamp in order to minimize the surge of current which occurs when the circuit is closed and thereby prevent destruction of the filament. Such a resistance is particularly useful withincandescent lamps used for projection and photographic purposes which are normally operated at a high over-load.

One of the objects of the present invention is to provide a resistance of a special type which will increase and make more uniform the lifeof such incandescent lamps. According to my invention, the lamp is provided with a resistance in series with the filament which is conductive at ordinary temperatures and has a high negative temperature-resistance coemcient, preferably considerably higher than that'of carbon.

Further features and advantages of my invention will appear from the following description of species thereof and from the drawing.

The drawing is an elevation of an incandescent lamp comprising my invention. The lamp comprises a bulb l0 which is preferably filled with an inert gas such as argon or nitrogen or a mixture thereof. The said bulb It) contains a filament ll, preferably of tungsten which has a positive temperature-resistance coefilcient. The filament Ii is connected tolead wires [2, l3, portions of which are sealed in the press portion ll of a stem tube IS. The said filament II is supported by wires ii, the ends of which are embedded in the end of an arbor I'I extending from the stem press I4. The lead wires i2, ii are electrically connected to the shell l8 and end contact l9 respectively, of a base 20. A short cylindrical. resistance body 2| is inserted in the lead wire ii in series with the filament Ii, being supported by a pair of suitable clamps 22.

The resistance body 2| consists of an oxide which is conductive at ordinary temperatures and has a high negative temperature-resistance coefllcient, such as a body of uranium dioxide. Such a resistance body not only prevents the 10 initial surge of current'through the filament ii when the circuit is closed, but because of its character and because it is placed in the bulb it which is filled with inert gas, it assures values of resistance which are always substantially the same, thereby resulting in a long and uniform lamp lite. Other oxides are also suitable for the resistance body providing they have sufllcient conductivity at ordinary room temperatures and their resistance remains the same over a wide range of voltages. V

What I claim as new and desire to secure b Letters Patent or the United States is:

1. An incandescent electric lamp comprising a bulb containing a filament having a positive temperature-resistance coefiicient and also containing a resistance electrically connected in series with said filament, said resistance consisting of an oxide which is conductive at ordinary temperatures and has a men negative temperatureresistance 'coefllcient.

2. An incandescent electric lamp comprising a bulb containing a filament having a positive temperature-resistance coefilcient and also containing a resistance body of uranium dioxide electrically connected in series with said filament.

"WILHEIMDUNKEL 

